First Book in Physiology and Hygiene eBook

9. In the circulation of the lungs, the blood
in the arteries is blue, that in the veins, red.

10. The change from blue to red takes place while
the blood is passing through the capillaries of the
lungs. The change is due to the oxygen which
the corpuscles of the blood take up in the lungs.

11. The pulse is caused by the beating of the
heart.

12. The heart does a great deal of work every
day in forcing the blood into different parts of the
body.

13. Some of the white blood corpuscles escape
from the blood-vessels through the thin walls of the
capillaries.

14. These corpuscles return to the heart through
small vessels called lymph channels or lymphatics.

15. The lymphatics in many parts of the body
run into small roundish bodies called lymphatic glands.

16. The object of the lymphatics is to remove
from the tissues and return to the general circulation
the lymph and white blood corpuscles which escape
through the walls of the capillaries.

CHAPTER XII.

HOW TO KEEP THE HEART AND THE BLOOD HEALTHY.

1. The heart is one of the most important of
all the organs of the body. If we take good care
of it, it will do good service for us during a long
life. Let us notice some ways in which the heart
is likely to be injured.

2. Violent Exercise.—­Did you
ever run so hard that you were out of breath?
Do you know why you had to breathe so fast? It
was because the violent exercise made your heart beat
so rapidly that the blood could not get out of the
lungs as fast as the heart forced it in. The lungs
became so filled with blood that they could not do
their work well. Sometimes, when a person runs
very fast or takes any kind of violent exercise, the
lungs become so filled with blood that a blood-vessel
is broken. The person may then bleed to death.
It is very unwise to overtax the heart in any way,
for it may be strained or otherwise injured, so that
it can never again do its work properly.

3. Effects of Bad Air.—­Bad
air is very harmful to the heart and to the blood
also. We should always remember that the blood
of the body while passing through the lungs is exposed
to the air which we breathe. If the air is impure,
the blood will be poisoned. In churches and in
other places where the air becomes foul, people often
faint from the effects of the impure air upon the
heart. It is important that the air of the rooms
in which we live and sleep should be kept very pure
by good ventilation.

4. Effects of Bad Food.—­The
blood is made from what we eat, and if we eat impure
and unwholesome food, the blood becomes impure.
We ought to avoid the use of rich or highly-seasoned
foods, candies, and all foods which are not nutritious.
They not only injure the blood by making it impure,
but they cause poor digestion.